This invention relates to an air conditioner for automobiles and more particularly to a blowout temperature control apparatus for stable control of blowout temperatures.
A blowout temperature control apparatus of an air conditioner for automobiles serves to control blowout temperatures of air blowing in the passenger room. In the past, as disclosed in U.S. Pat. No. 4,757,944 to Kagohata et al, this type of blowout temperature control apparatus has been proposed wherein a plurality of outlet ports are provided at which temperatures can be controlled independently, and temperature sensors sensors for detection of the blowout temperatures (called duct sensors) are disposed at the respective outlet ports, whereby the opening of each air mixing door is controlled such that the difference between a signal from an associated duct sensor and a blowout temperature calculated in advance approaches zero, thereby ensuring that the blowout temperature can be controlled independently at each outlet port in compliance with individual blowout modes without using any feedback potentiometer.
Further, JP-A-58-145515 by Hitachi, Ltd., filed in Japan on Feb. 24, 1982, has proposed a temperature control apparatus wherein when the thermal load is large and sufficient cooling capability is required therefor, a water cock for regulation of the flow rate of hot water flowing into a heater core is closed to stop the flow of hot water into the heater core, causing the heater core not to depress cooling capability and consequently maintaining the sufficient cooling capability.
The first prior art however fails to consider that the position of the air mixing door 11 during the blowout mode being the ventilation mode is always uncertain. More particularly, since in the aforementioned blowout mode the floor duct sensor 103L does not receive blowout air, this sensor 103L detects ambient temperatures not related directly to the blowout temperature and the opening of the air mixing door 11 is controlled on the basis of a detected temperature to cause the air mixing door 11 to behave unstably. Under this condition, when the blowout mode changes from the aforementioned ventilation mode to another mode such as bi-level mode or floor/ventilation mode to be described later, uncomfortable blowout temperatures disadvantageously take place temporarily before the floor duct sensor 103L detects a proper blowout temperature to control the opening of the air mixing door 11 to a suitable value.
Further, when the second prior art, JP-A-58-145515 is applied to the blowout mode being the ventilation mode or the floor/ventilation mode for which maintenance of cooling capability is required, air conditioning is carried out under the condition that the water cock 16 for regulation of the amount of hot water flowing in the heater core 3 is closed and therefore, after coincidence of the blowout temperature with a target value, air conditioning is effected with the heater core 3 sufficiently cooled. Under this condition, even if the blowout air temperature is desired to be raised and the air mixing door is moved toward "Hot", the blowout air temperature will not rise because the heater core 3 is cooled sufficiently as described above, and the air mixing door continues moving toward "Hot". At that time, when the blowout mode changes to, for example, the bi-level to comply with changes in outside air temperature Ta and insolation amount Zm, the water cock 16 is abruptly opened for heating and a large amount of hot water follows into the heater core 3 to abruptly heat it up. Then, with the air mixing door moved toward "Hot" as described hereinbefore, uncomfortable blowout temperatures disadvantageously take place temporarily before control of the air mixing door to a suitable opening it completed.
One may also refer to U.S. Pat. No. 4,829,884 to Kagohata which discloses control of blowout temperature effected on the basis of signals from individual blowout air temperature detecting means.
Continuous switching of the blowout mode and blowout temperature control without resort to any potentiometer for detection of air mixing door position which are relevant to the present invention are also described in U.S. patent application Ser. No. 93228 filed September, 1987.